Optical transducer with integrated feedthrough

ABSTRACT

An optical transducer is provided. A “measuring” portion of the transducer may be exposed to a high pressure and fluids when the optical transducer is deployed (e.g., in a wellbore or other industrial setting). The transducer may include an optical waveguide with a first portion that forms a first seal that isolates an “instrumentation” portion of the transducer from exposure to the high pressure and fluids to which the measuring portion may be exposed. The transducer may also include a second seal with a “stack” of material elements that contact a second portion of the optical waveguide to also isolate the instrumentation portion of the transducer from exposure to the high pressure and fluids to which the measuring portion may be exposed.

CLAIM OF PRIORITY UNDER 35 U.S.C. §119

This application claims benefit of U.S. Provisional Patent ApplicationNo. 61/608,569, filed Mar. 8, 2012 and entitled “Optical Transducer withIntegrated Feedthrough,” which is herein incorporated by reference inits entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the invention generally relate to feedthroughs and, moreparticularly, to feedthroughs suitable for use in high pressure, hightemperature, and/or other harsh environments.

2. Description of the Related Art

Many industries and applications utilize apparatus sensors to measureparameters, such as pressure. In some cases, such sensors may utilizeoptical waveguides that are designed to penetrate a wall, bulkhead, orother feedthrough member wherein a relatively high fluid differentialpressure exists across a feedthrough member. In addition, one or bothsides of the feedthrough member may be subjected to relatively hightemperatures and other harsh environmental conditions, such as corrosiveor volatile gases, liquids, and other materials. For example, a bulkheadfeedthrough may call for sealing an optical waveguide at high pressuresof about 138,000 kilopascal (kPa) and above, and high temperatures ofabout 150° C. to 300° C. and above, with a service life of 5 to 20 ormore years.

Several challenges exist with constructing a sensor utilizing such anoptical fiber feedthrough. One of these problems involves thesusceptibility of the glass fiber to damage and breakage due to itssmall size, flexibility, and brittle nature. Another challenge involvesthe potential for leaks when the optical fiber is sealed in afeedthrough bore using epoxy or other bonding materials, which may crackwhen exposed to an extreme range of temperatures and pressures.

SUMMARY OF THE INVENTION

Embodiments of the invention generally relate to feedthroughs (e.g.,feedthroughs for optical sensors, slickline, wireline, otherelectrically or optically conductive lines or pathways, and the like)suitable for use in high pressure, high temperature, and/or other harshenvironments.

For some embodiments, an optical transducer is provided. A “measuring”portion of the transducer may be exposed to a high pressure, hightemperature fluids when the optical transducer is deployed (e.g., in awellbore or other industrial setting). The transducer may include anoptical waveguide with a first portion that forms a first seal thatisolates an “instrumentation” portion of the transducer from exposure tothe high pressure and fluids to which the measuring portion may beexposed. The transducer may also include a second seal with a “stack” ofmaterial elements that contact a second portion of the optical waveguideto also isolate the instrumentation portion of the transducer fromexposure to the high pressure and fluids to which the measuring portionmay be exposed.

Together, the first and second seals may be considered to form primaryand secondary seals, providing redundancy and some assurance of sealing(backup) even in the case where one seal is breached. Which isconsidered primary or secondary may be relatively arbitrary. Exactmaterials of various components of the transducer may be selected basedon the desired pressure performance and the temperature criteria. Forexample, the second seal may include a stack of two or more (possiblyalternating) materials selected to achieve a desired temperatureperformance while still maintaining the integrity of their shape foradequate sealing.

One embodiment of the present invention provides an optical transducer.The optical transducer generally includes at least one opticalwaveguide; at least one sensing element formed in a portion of theoptical waveguide; and a feedthrough element designed to isolate a firstportion of the transducer in communication with the sensing element froma second portion of the transducer containing the sensing element,wherein the feedthrough element comprises at least a first seal formedby a first portion of the optical waveguide in contact with a boreextending through a housing of the feedthrough element and a second sealformed by contact between an arrangement of sealing elements with asecond portion of the optical waveguide and an inner surface of thefeedthrough housing.

Another embodiment of the present invention provides an opticaltransducer. The optical transducer generally includes at least oneoptical waveguide; at least one sensing element disposed in a portion ofthe optical waveguide; and a feedthrough element designed to isolate afirst portion of the transducer in communication with the sensingelement from a second portion of the transducer containing the sensingelement, wherein the feedthrough element comprises a seal formed by afirst portion of the optical waveguide in contact with a bore extendingthrough a housing of the feedthrough element and wherein a portion of amating surface of the bore for forming the seal is undercut to reduce atleast one of a magnitude or a gradient of a stress distribution in aregion transitioning from high stress to no stress along the firstportion of the optical waveguide.

Yet another embodiment of the invention provides a feedthrough assembly.The assembly generally includes at least one conductive line and afeedthrough element designed to isolate a first portion of the assemblyfrom a second portion of the assembly, wherein the feedthrough elementcomprises a first seal formed by a first portion of the line in contactwith a bore extending through a housing of the feedthrough element andwherein a portion of a mating surface of the bore for forming the firstseal is undercut to reduce at least one of a magnitude or a gradient ofa stress distribution in a region transitioning from high stress to nostress along the first portion of the line. The at least one conductiveline may include at least one of an optical waveguide or a wireline. Forsome embodiments, a pre-loading force is applied to promote sealing ofthe first seal prior to deployment in an operating environment. For someembodiments, the feedthrough element also includes a second seal formedby contact between an arrangement of sealing elements with a secondportion of the line and an inner surface of the feedthrough housing.

Yet another embodiment of the invention provides a feedthrough assembly.The assembly generally includes at least one conductive line and afeedthrough element designed to isolate a first portion of the assemblyfrom a second portion of the assembly, wherein the feedthrough elementcomprises at least a first seal formed by a first portion of the line incontact with a bore extending through a housing of the feedthroughelement and a second seal formed by contact between an arrangement ofsealing elements with a second portion of the line and an inner surfaceof the feedthrough housing.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a cross-sectional diagram of an optical transducer with anintegrated feedthrough, according to embodiments of the invention.

FIG. 2 is a cross-sectional diagram of the feedthrough portion of theoptical transducer shown in FIG. 1, according to embodiments of theinvention.

FIG. 3 illustrates an example stack of materials for a dynamic seal,according to embodiments of the invention.

FIG. 4 is a cross-sectional diagram of an example pre-loaded portion ofthe transducer illustrated in FIG. 1, according to embodiments of theinvention.

FIG. 5 illustrates an example exterior view of the portion of thetransducer illustrated in FIG. 4, according to embodiments of theinvention.

FIG. 6 illustrates an example final assembly of a transducer, accordingto embodiments of the invention.

DETAILED DESCRIPTION

Embodiments of the invention generally relate to feedthrough assembliesapplicable for use in high temperature, high pressure environments.While transducers with optical waveguide feedthrough assemblies aredescribed in detail below, embodiments of the invention also apply toother types of feedthroughs (e.g., wireline feedthrough assemblies,where wireline for electrical communication, logging, or running andretrieving downhole tools is isolated from harsh environments).

According to some embodiments, an optical transducer may incorporate afeedthrough assembly having a first seal formed by a frustoconical glassplug disposed in a recess (e.g., a counterbore) of a feedthroughhousing. The glass plug may define a large-diameter, cane-based,waveguide sealed within the recess in the housing and providing opticalcommunication through the housing. All embodiments described hereinprovide for sealing with respect to the housing at or around the glassplug as the glass plug is brought into contact with a sealing surface ofthe recess.

As used herein, “optical fiber,” “glass plug,” and the more general term“optical waveguide” refer to any device for transmitting optical signalsalong a desired pathway. For example, each of these terms can refer tosingle mode, multi-mode, birefringent, polarization-maintaining,polarizing, multi-core or multi-cladding optical waveguides, or flat orplanar waveguides. The optical waveguides may be made of any glass(e.g., silica, phosphate glass, or other glasses), glass and plastic, orsolely plastic. Furthermore, any of the optical waveguides can bepartially or completely coated with a gettering agent and/or a blockingagent (such as gold) to provide a hydrogen barrier that protects thewaveguide.

FIG. 1 shows an example optical transducer 100 incorporating afeedthrough (F/T) element 105 that isolates a first (measuring) portion110 of the transducer from a second (instrumentation) portion 120 of thetransducer. The measuring portion 110 of the transducer may be used tosense a parameter (e.g., temperature or pressure) and convert the sensedparameter to a varying optical signal. The instrumentation portion 120may provide an interface for sending the optical signals to electronicsensing equipment via a connector and an optical cable having one ormore optical fibers.

As illustrated, according to certain aspects, the transducer 100 may bea pressure transducer, and the measuring portion 110 may include apressure foot and bellows assembly 130, which may move axially inresponse to external pressure, thereby transferring pressure changes toa filling fluid inside of the bellows assembly and to a sensing element.The sensing element may be formed from an optical waveguide having oneor more Bragg gratings formed therein. The pressure changes in thefilling fluid may cause a change in a grating wavelength. One or moresecond gratings may be isolated from changes in pressure or configuredto respond with different sensitivities, providing for unique andseparated values of the pressure and temperature changes via solutionsto the resulting system of multiple equations.

The sensing element may be contained in a filling fluid (e.g., siliconeoil) providing some protection and dampening, as well as transferringthe pressure changes to the sensing element. As illustrated, thisportion may be filled via an integrated fill port 140, which may besealed to ensure no communication between the environment (e.g.,wellbore fluids) outside of the transducer and the housing containingthe filling fluid. In some cases, this sealing may be accomplished by asealing element and, for some embodiments, by a threaded element. Thethreaded element may provide reinforcement of the sealing element andmay act as a backup seal to contain any leaks if the sealing elementfails.

As shown in FIG. 2, a sealing portion 204 of the optical waveguide 200may be conical (or frustoconical) shaped and mate with a complementaryshaped mating surface of a bore in a metal housing 202, thereby forminga glass-to-metal seal 203. Naturally occurring pressure duringdeployment and operation (e.g., within a wellbore) may force the sealingportion 204 towards the mating surface forming a seal. As will bedescribed in greater detail below, a mechanism may also be provided to“pre-load” the glass-to-metal seal 203 during fabrication of thetransducer 100, prior to transportation and deployment.

For some embodiments of the invention, an element, such as a thin washer306 (illustrated in FIG. 3), may be used between the sealing portion 204and the mating surface of the housing 202 to promote sealing (e.g., byfilling in any imperfections between the sealing surfaces, as well asalleviating the concentration of contact stresses). The washer 306 maycomprise any suitable material for aiding the glass-to-metal seal 203,such as a relatively soft metal (e.g., gold).

As described above, the optical waveguide 200 in the instrumentationportion 120 may be connected with an optical cable for sending theoptical signals to electronic sensing equipment. Similarly, in awireline feedthrough assembly, for example, the one or more wirelinesmay pass through the feedthrough element's housing and couple with aconnector and an electrical cable having one or more wires for sendingthe electrical signals traversing the wirelines to electronic equipment.

Unlike conventional feedthrough optical transducers, the opticalwaveguide 200 is a monolithic structure providing both the sensing andthe feedthrough aspects. In contrast, conventional transducers typicallyinclude two separate components to achieve these aspects: a sensingoptical waveguide and a separate feedthrough glass plug, connected withthe sensing waveguide via an optical fiber jumper. Furthermore, theoptical fiber jumper is exposed to high pressures and potentiallyharmful fluids in conventional designs. The removal of such a jumperfiber from embodiments of the invention reduces the risks of performancefailures.

When axially loading elements of brittle materials, such as glass as inthe present example, stresses may be relatively linear across the matingsurfaces of the elements before abruptly encountering a regiontransitioning from “high compression stress” to “no stress” at the endof the mating surface. This abrupt transition may result in aconcentration of tensile stress at this region, which may lead tobrittle material distortion and, ultimately, breakage. According tocertain aspects, however, the magnitude and gradient of the transitionalstress distribution may be reduced as shown in FIG. 2, by removing(e.g., undercutting) a portion of the mating surface of the housing 202,such that a gap 206 is created when the glass plug is seated in acomplementary counterbore of the housing. This removal may be performed,for example, by undercutting the housing 202 along an inner ring of thebore's mating surface. In this case, the resulting surface of thehousing 202 opposite the counterbore may have an annular undercut, asillustrated in FIG. 2. For other embodiments, the reduction in themagnitude and gradient of the transitional stress distribution may beaccomplished by casting or otherwise forming a housing 202 initiallyhaving an annular undercut opposite the counterbore, such that removalneed not be performed. This reduction of the magnitude and gradient ofthe transitional stress distribution from high compression to nocompression may help prevent breakage. In the case of the transducer100, this modification of the mating surface removes a failure mode,thereby increasing the reliability and lifetime of the transducer.

As illustrated in FIG. 2, the feedthrough element 105 may also includeone or more dynamic seals (commonly referred to as “chevron” seals orv-seals due to their “v” shape in cross section) as a second sealingfeature. In an assembled product, these dynamic seals may contact asecond portion of the optical waveguide 200 and the housing 202,providing backup to the glass-to-metal seal 203 (or the glass-to-metalseal could be viewed as providing backup to the dynamic seals). Asgreater pressure is applied, the dynamic seals are compressed axiallyand further expanded radially, thereby tightening the seal between theoptical waveguide 200 and housing 202. Furthermore, the dynamic sealsmay also centralize the optical waveguide 200 within the transducer 100,relative to the bore of the feedthrough housing 202 and to theglass-to-metal seal 203.

As previously described, exact materials of various components of thetransducer 100 may be selected based on desired performance andtemperature criteria. For example, the second sealing feature mayinclude a “stack” 300 of two or more (possibly alternating) materials302, 304 as shown in FIG. 3. The material 302, 304 may be selected toachieve desired temperature performance while still maintainingintegrity of their shape for adequate sealing. Examples of suchmaterials may include PEEK, Teflon, a polyimide, and other polymers. Insome cases, for a relatively high temperature rating (e.g., up to 250°C.), a transducer may include a stack of alternating PEEK and Teflon. Aneven higher temperature rating (e.g., >300° C.) may be achieved byutilizing graphite, graphite-reinforced polymers, or certain highperformance polyimides, such as PMR-15, in the stack 300. Of course,general substitutions between materials may be made, as appropriate, andmaterials of other parts may also be replaced to increase thetemperature rating and the reliability.

Another feature that increases the temperature rating and thereliability of the transducer 100 is the lack of epoxy or other bondingmaterial used in the measurement portion 110. Conventional opticalfeedthrough designs typically expose epoxy used as a sealing feature inthe measurement portion 110 to high temperatures. However, thestructural integrity of epoxy can fail at such high temperatures,thereby leading to unacceptable leaks in the seal. With theglass-to-metal seal 203 and/or the dynamic seals in embodiments of thepresent invention, epoxy need not be used in the transducer 100.

Material removals to reduce the magnitude and gradient of stressdistributions at component interfaces, as described above, may also beutilized in the pre-loaded portion 400 of the transducer 100 shown inFIG. 4. As illustrated, a shape of the waveguide 200 may be designed toallow an axial force 406 to be applied to the waveguide during theassembly process. This pre-loading may help maintain contact in theglass-to-metal seal 203 before exposure to operating pressure. However,the stress concentrations that develop in the contact areas between thewaveguide 200 and one or more members 402 (e.g., a clamp) used to applyforce during pre-loading may result in damage to the optical waveguide.Therefore, as illustrated in FIG. 4, one or more portions 404 of amember 402 may be removed (e.g., undercut) in an effort to reduce themagnitude and gradient of stress concentrations imposed on the waveguide200 during pre-loading. The members 402 may be composed of any suitablematerial, such as plastic, and may be held in place by a collar in thepre-loaded portion 400.

For some embodiments, an axial pre-loading force may also be applied tothe stack 300 during fabrication of the transducer 100. This pre-loadingforce may be used to axially compress and radially expand the dynamicseals and create the seal between the optical waveguide 200 and thehousing 202. For some embodiments, the pre-loading force may be suppliedby a v-seal pre-loader 208, as illustrated in FIGS. 2 and 4.

According to certain aspects, one or more diagnostic sensors (e.g.,Bragg gratings) may be utilized to monitor the amount of force appliedduring pre-loading. In some cases, such a diagnostic sensor may beplaced in any suitable position along the waveguide 200 that is subjectto the pre-loading forces, such as between the pre-loaded portion 400and the sealing portion 204 of the optical waveguide 200. Such adiagnostic sensor may, for example, be monitored during the pre-loadingand utilize a different wavelength band than the sensors used in thesensing element.

FIG. 5 illustrates an exterior view of the pre-loaded portion 400depicted in FIG. 4. The pre-loaded portion 400 may include a pre-loaderhousing 500 that surrounds the optical waveguide pre-loaded with the useof the member(s) 402. A flange 504 of the pre-loader housing may beretained axially by one or more retention members of the v-sealpre-loader 208, such as the bayonet-shaped members 502 shown in FIG. 5.Retention of the pre-loader housing in this manner allows the housing tobe radially shifted, such that a center of the housing may be disposedon-axis or slightly off-axis with respect to the bore of the housing 202(and the axis of the v-seal pre-loader 208). With this potential radialshift of the pre-loader housing, a bending force on the opticalwaveguide 200 is avoided, or at least reduced, during assembly of thetransducer 100. Minimizing this bending force avoids stressing theoptical waveguide, such that shock loads do not crack the opticalwaveguide and lead to transducer failure.

During transducer assembly, the pre-loader housing may be disposed abovethe v-seal pre-loader 208 to surround the members 402, rotated such thatthe flange 504 is retained by the members 502, and positioned radiallyin an effort to avoid, or at least reduce, bending forces on the opticalwaveguide 200. Then, the flange 504 of the pre-loader housing may bewelded in position above the v-seal pre-loader 208. Should the flangewelds fail during operation of the transducer, the members 502 preventthe pre-loader housing 500 from moving axially away from the v-sealpre-loader 208.

FIG. 6 illustrates an example final assembly of a transducer 600 inaccordance with aspects of the present disclosure. Installation of thecompleted assembly may be relatively straightforward, for example, withthe pressure foot of the sensing portion bolted onto a mandrel pressureport in an area to be measured. Connections for instrumentation may bemade on the instrumentation side 602, with isolation from the measuredenvironment provided by the sealing features described above.

Embodiments of the invention offer several advantages over conventionaloptical transducers with feedthrough features. For example, transducersdescribed above may achieve a higher long-term operating temperature (atleast 200° C., and in some cases in excess of 300° C.) than conventionaltransducers, which typically fail above 150° C. (e.g., due to breakdownof the epoxy, glue, or other bonding material). With the use of thebellows assembly in the measurement portion of the transducer, anyoptical fiber or other glass components are isolated from harmfulfluids. Furthermore, the features described above for reducing oreliminating damage to brittle materials lead to significantly loweredrisk of failure during transportation, deployment, and operation of thetransducer. Overall, the various attributes described above lead tofeedthrough optical transducers with increased reliability and lifetimescompared to conventional feedthrough transducers.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. An optical transducer, comprising: at leastone optical waveguide; at least one sensing element disposed in aportion of the optical waveguide; a feedthrough element designed toisolate a first portion of the transducer in communication with thesensing element from a second portion of the transducer containing thesensing element, wherein the feedthrough element comprises: a first sealformed by a first portion of the optical waveguide in contact with abore extending through a housing of the feedthrough element; and asecond seal formed by contact between an arrangement of sealing elementswith a second portion of the optical waveguide and an inner surface ofthe feedthrough housing; and a member in contact with a third portion ofthe optical waveguide and configured to apply a first pre-loading forceto promote sealing of at least the first seal, wherein the third portionof the optical waveguide has a greater outer diameter than the first andsecond portions of the optical waveguide.
 2. The optical transducer ofclaim 1, wherein a second pre-loading force promotes sealing of thesecond seal by expanding the sealing elements.
 3. The optical transducerof claim 1, further comprising a diagnostic grating disposed in theoptical waveguide allowing the first pre-loading force to be measured.4. The optical transducer of claim 1, wherein a portion of a surface ofthe member is undercut to reduce at least one of a magnitude or agradient of a stress distribution in a region transitioning from highstress to no stress along the third portion of the optical waveguide. 5.The optical transducer of claim 1, wherein the member is configured toapply the first pre-loading force such that a bending force on theoptical waveguide during assembly is avoided.
 6. The optical transducerof claim 1, wherein a portion of a mating surface of the bore forforming the first seal is undercut to reduce at least one of a magnitudeor a gradient of a stress distribution in a region transitioning fromhigh stress to no stress along the first portion of the opticalwaveguide.
 7. The optical transducer of claim 1, wherein the sealingelements comprise at least two elements, alternating between at leasttwo materials.
 8. The optical transducer of claim 7, wherein at leastone of the two materials comprises a polymer.
 9. The optical transducerof claim 7, wherein at least one of the two materials comprises PMR-15,graphite, or a graphite-reinforced polymer.
 10. The optical transducerof claim 7, wherein the at least two materials comprise PEEK and Teflon.11. An optical transducer, comprising: at least one optical waveguide;at least one sensing element disposed in a portion of the opticalwaveguide; a feedthrough element designed to isolate a first portion ofthe transducer in communication with the sensing element from a secondportion of the transducer containing the sensing element, wherein: thefeedthrough element comprises a seal formed by a first portion of theoptical waveguide in contact with a bore extending through a housing ofthe feedthrough element; and a portion of a mating surface of the borefor forming the seal is undercut to reduce at least one of a magnitudeor a gradient of a stress distribution in a region transitioning fromhigh stress to no stress along the first portion of the opticalwaveguide; and a member in contact with a second portion of the opticalwaveguide and configured to apply a pre-loading force to promote sealingof the seal, wherein the second portion of the optical waveguide has agreater outer diameter than the first portion of the optical waveguide.12. The optical transducer of claim 11, further comprising a diagnosticgrating disposed in the optical waveguide allowing the pre-loading forceto be measured.
 13. The optical transducer of claim 11, wherein aportion of a surface of the member is undercut to reduce at least one ofa magnitude or a gradient of a stress distribution in a regiontransitioning from high stress to no stress along the second portion ofthe optical waveguide.
 14. The optical transducer of claim 11, whereinthe pre-loading force is applied such that a bending force on theoptical waveguide during assembly is avoided.
 15. A feedthroughassembly, comprising: at least one conductive line; a feedthroughelement designed to isolate a first portion of the assembly from asecond portion of the assembly, wherein the feedthrough elementcomprises a first seal formed by a first portion of the line in contactwith a bore extending through a housing of the feedthrough element andwherein a portion of a mating surface of the bore for forming the firstseal is undercut to reduce at least one of a magnitude or a gradient ofa stress distribution in a region transitioning from high stress to nostress along the first portion of the line; and a member in contact witha second portion of the line and configured to apply a pre-loading forceto promote sealing of the first seal, wherein the second portion of theline has a greater outer diameter than the first portion of the line.16. The assembly of claim 15, wherein the line comprises at least one ofan optical waveguide or a wireline.
 17. The assembly of claim 15,wherein the feedthrough element further comprises a second seal formedby contact between an arrangement of sealing elements with a thirdportion of the line and an inner surface of the feedthrough housing. 18.The optical transducer of claim 5, further comprising another housingsurrounding the member and the third portion of the optical waveguide,wherein the other housing is retained axially in a manner allowing acenter of the other housing to be shifted radially with respect to acenter of the bore of the feedthrough housing to avoid the bending forceon the optical waveguide during assembly.
 19. The optical transducer ofclaim 18, wherein the other housing comprises a flange configured to beretained axially by one or more bayonet-shaped retention members. 20.The optical transducer of claim 1, wherein the third portion of theoptical waveguide is flared.